City officials say the boil order affects residents east of the Reversing Falls Bridge, with the exception of the Millidgeville area.
However, people in that neighbourhood are asked to conserve water until the boil order is lifted.
The city says there was a failure in the chlorination system at the Latimer Lake Water Treatment Facility on Friday morning.
It says the failure means water is not being disinfected.
The order will remain in place until further notice.